NO. 3 



COMPARATIVE HISTOLOGY OP FEMUR FOOTE 



121 



of the section and in the posterior and outer wall about one-fourth of the entire 

 thickness. They are frequently interrupted by crude Haversian systems of the 

 (la) differentiation and crossed at various angles by short canals. Their lacuna; 

 and canaliculi are well developed. The central ring is composed of well de- 

 veloped Haversian systems and lamella? with systems of the (la) differentiation. 

 The ring is widest in the outer lateral wall. 



In the lamellar portion of the ring are one or two concentric rows of 

 small Haversian canals which gradually change into the more completely 

 developed Haversian systems of the outer wall. The internal circumferential 

 lamella?, surround the medullary canal excepting in the outer wall. The lamellar 

 and Haversian portions of the section are about equal. 



Type I-III, la, C. 



RIGHT FEMUR OF MIDAS RUFONIGER. SOUTH AMERICAN MONKEY ( UPPER AMAZON ) . 



NO. 14548, U. S. NAT. MUS. 



Pl. 15, Tig. 212. Syn. Tab. VI 



Antero-posterior diameter of bone, 4.5 mm.; lateral, 4 mm. 

 Antero-posterior diameter of medullary canal, 3 mm.; lateral, 2.5 nun. 

 The medullary canal is full. Medullary index, 74%. 



Structure. — The three structural rings are distinctly marked. The external 

 circumferential lamella? form a thick enclosing ring of one-third to one-half the 

 thickness of the wall of the bone. The lamella; of the inner wall are very fre- 

 quently dotted with small, clear, round spaces which are not present in the 

 outer wall. The lacuna? are well developed. 



The central ring is composed of rather irregularly shaped but well de- 

 veloped Haversian systems, separated by inter-Haversian lamella?. They are 

 frequently united by canals. The internal circumferential lamella? form a nar- 

 row ring around the medullary canal, excepting in the outer wall where they 

 are deficient. 



Type I-III, la, C. 



LEFT FEMUR OF LEMUR. NO. 84383, U. S. NAT. MUS. 



Pl. 15, Fig. 243. Syn. Tab. VI 



Antero-posterior diameter of bone, 10 mm. ; lateral, 8.5 mm. 

 Antero-posterior diameter of medullary canal, 5.5 mm. ; lateral, 4.5 mm. 

 The medullary canal is full. Medullary index, 41%. 



Structure. — The section is surrounded by a lamellar ring which is widest 

 in the anterior and posterior wall. In the inner wall it is divided into lamina?, 

 and frequently interrupted by canals and very crude Haversian systems of the 

 (la) differentiation. The lacuna? are generally well developed. The central 



